1. Field of the Invention
The invention relates to a method for surface processing of a continuously cast steel product in the hot state for the removal of surface flaws, surface contaminants etc. Moreover, the invention relates to a device therefore, as well as an arrangement for manufacturing strips and sheets with a device for surface treatment integrated in the process. In the context of this invention the cast product is not limited to a certain thickness or geometry.
2. Description of the Related Art
Basically, the surface processing of sheets and strips of steel after rolling in the cold state is known, for example, by pickling. During solidification of continuous cast products, especially products of stainless steel alloys or acid-resistant steel alloys or RAH (rust, acid and heat resistant) qualities, an outer skin is however formed which, on the one hand, can have geometric surface flaws or markings and, on the other hand, can contain contaminants of segregation, oxides, and casting powder residues. It is therefore desirable to remove these before rolling in order to satisfy highest product requirements of the surface properties of the rolled strips and sheets.
From EP 0 435 897 B1 a method for grinding ingots, slab, or similar workpieces of metal is known in which surface flaws or surface contaminants are removed in the hot state. Advantages of these preceding grinding processes performed in the hot state, i.e., in direct connection with casting, continuous casting, rolling, or a different type of hot forming, is that the material is ground before scaling can occur on the surface due to cooling which must be removed in the cold state in addition to the surface flaws. A certain temperature interval for employing grinding methods is indicated whose lowest limit value is the temperature at which essentially a scaling layer is not yet formed. The upper limit value is determined by the composition of the grinding belt, i.e., by the highest temperature at which the strip is not thermally disadvantageously affected. It is suggested to increase the service life of the grinding belt by increasing the rotational speed. Even though, the use of the grinding belt is limited to the provided temperature interval. Moreover, despite increase of the rotational speed it cannot be excluded that the belt, due to the high temperatures of the product to be ground and due to the resulting frictional energies, will melt or burn. The disadvantageous consequences are smudging or residues of the damaged belt on the metal surface.
From DE 30 37 571 A1 a method for mechanical removal of material from continuous cast surfaces in the hot state is also known wherein the hot strand, before being transversely cut, is ground with grinding wheels moving back and forth between the strand edges simultaneously on the top surface and bottom surface. The grinding wheel however does not reach a long service life.
It is an object of the present invention to provide a method and a device with which a surface processing of continuously cast steel products for removal of surface flaws in the hot state can be achieved by using surface processing devices not necessarily adjusted to high temperatures while achieving a long service life.
In accordance with the present invention, this is achieved in that, prior to the step of surface treatment, a cooling of at least a part of at least one surface of the metal product is performed for a defined temperature reduction of the surface to be processed. The suggested device accordingly provides a corresponding cooling means.
As a consequence of the step according to the invention of a partial cooling, i.e., a surface near cooling, the processing tools for surface treatment are thermally less loaded than in the methods according to the prior art. It is even possible to employ temperature sensitive processing methods and such methods that are not designed for high temperatures because, due to the preceding partial temperature reduction, the service life of the tools, for example, grinding belts or grinding wheels, is increased. A disadvantageous decomposition of the grinding belt with smudging of the residues on the metal surfaces or bursting of the grinding wheels does not occur.
The directed temperature reduction is therefore limited to the surface of the metal product and advantageously adjusted such that the processing resistance of the workpiece is not influenced in an undesirable fashion. According to the inventive method, all surfaces of the metal product, for example, of a thin slab portion, i.e., the underside and top side as well as the lateral surfaces, can be cooled. However, it is also conceivable that only one surface, for example, only the top surface of the metallic product is cooled or only defined portions of surfaces.
According to the suggested method surface treatments of all types, geometries, and thicknesses of cast products are conceivable, and the method is not limited to the use of slabs or thin slabs for producing sheets and strips.
According to a preferred embodiment is suggested that the steps of surface cooling and surface processing is preceded by an inspection of at least one portion of the surface of the metallic product with respect to surface flaws or contaminants and, based on the result of the inspection, a selective surface processing only of the surface areas which have been detected as having a flaw takes place. As with the partial cooling, the inspection can be performed on all surfaces or only on portions thereof. The subsequent partial cooling of the surface is carried out preferably continuously, but conceivable is also a cooling action limited to the areas which have been found to have flaws which requires a corresponding operative excess expenditure and a subsequent consideration of the temperature differences within the surface.
According to a further preferred embodiment, it is suggested that a cleaning or descaling process is performed directly upstream of the surface processing arrangement with the step sequence of surface inspection, partial cooling of the surfaces, as well as surface treatment. By means of the descaling process an additional cooling action results, and, moreover, possibly already formed scaling or surface contaminants already present are removed and a suitable basis for the inspection of the surface is provided.
Overall, all known methods for surface treatment can be employed, such as, for example, grinding, milling, or flame chipping. In particular, grinding can be employed with use of known tools such as grinding belts, grinding wheels, or grinding stones with different type of grains and grain size.
In the known embodiments it is possible to process the underside and top side and/or the lateral surfaces of the cast product that is, for example, in the form of slab or thin slab, simultaneously as well as successively. For a simultaneous treatment, the processing time is reduced and the energy expenditure is kept at a low level, in particular, since the surface removal is carried out in the hot state in which the removal can be performed with a reduced energy expenditure in comparison to the cold state.
Preferably, the surface treatment on the partially cooled surfaces, together with the preferably suggested preparative method steps, is carried out for the continuously cast steel product preferably between the casting process and thexe2x80x94preferably directly successively performedxe2x80x94rolling process. The surface treatment is either integrated inline in this production line (X) or is carried out offline in a branch line (Y).
Different embodiments of the surface processing devices or arrangements result from the different compositions of individual devices (cooling devicexe2x80x94inspection devicexe2x80x94cleaning device) as well as in the case of a direct casting and rolling method from the different sequences of the buffering, compensation, or heating furnaces in an inline or offline version. For example, a device for cooling at least one part of at least one surface of the metal product is arranged upstream of the device for surface treatment of the metal product.
Preferably, the cooling device has an inspection device for detection of flawed surface areas arranged upstream thereof.
The inspection device may have a cleaning device, preferably a descaling device, arranged upstream thereof.
The arrangement for producing sheets and strips of metal comprises a continuous casting device for casting slabs, preferably of a thickness between 30 and 250 mm, optionally a transverse separating device, a heating arrangement of a heating device and/or a temperature compensation device, a hot mill train, as well as a device for surface processing as explained above.
The surface processing device is arranged upstream and/or downstream of the heating device and/or a temperature compensation device in the conveying direction of the slab within the production line.
The arrangement comprises a branch line, arranged parallel to the heating device and/or a temperature compensation device or portions thereof, and slab portion carriages configured to move the slab portions from the production line to the branch line and back, wherein the slab portion carriages are arranged before and behind the heating device and/or a temperature compensation device or portions thereof.
The branch line further comprises a temperature equilibration furnace or a heating furnace downstream of the surface treatment device.
Preferably, a buffer furnace is arranged upstream of the surface treatment device.
The method according to the invention is preferably used for surface processing of rust-resistant (stainless) and acid-resistant steel products.